1. Field of the Invention
The present invention relates to apparatuses for extracting cataractous tissue and, in particular, to wedge-shaped probes for phacoemulsification, for removal of soft cataractous tissue, and for cortical clean-up.
2. Description of the Art
The human eye includes an anterior chamber and a posterior chamber which are separated by a normally transparent lens which performs the function of focussing light onto the retina defined along the rear wall of the posterior chamber. The lens can become cloudy for any of a variety of reasons which results in the impairment of vision. The cloudy lens must then be removed and replaced with an intraocular lens (IOL) implant. In the alternative, thick glasses or contact lenses can be used to properly focus light onto the retina.
Many techniques are now used for removing the cloudy, cataractous lens material. One of those techniques is phacoemulsification. With this technique a small incision is made in the surface of the eye and a probe is inserted through that incision. The probe will typically include an irrigation passage for conveying irrigating fluid into the eye and an aspiration passage for removing cataractous tissue and the irrigating fluid from within the eye. The probes are coupled to a source of ultrasonic power and ultrasonic vibration is selectively applied to the probe to break up cataractous tissue which the probe contacts to facilitate aspiration of the same.
One significant advantage of phacoemulsification is that the incision in the eye can be smaller than with some other cataract lens removal techniques. There are numerous benefits to small incision surgery including small wound size, less post operative astigmatism, more controlled removal of cataractous material, earlier recovery of visual function and early ambulation of the patient.
One difficulty with phacoemulsification is that considerable problems are often encountered in mastering the skills needed to perform the procedure safely. However, even after the surgeon has become skilled in the phacoemulsification technique itself, conventional phaco handpieces present a number of difficulties which skill alone cannot remedy.
More particularly, conventional phacoemulsification probes are typically in the form of an elongated tube which terminates distally in a sharp planar end or a sharp pointed or sloped end. That tube defines the aspiration passage for removing cataractous tissue and fluid from within the eye. Thus, the aspiration port and passage have a diameter defined by the diameter of the tube, which is typically relatively large, on the order of 2 to 3 millimeters, and the aspiration passage has a generally constant bore along its entire length.
Irrigation fluid is typically provided via an irrigation sleeve provided in surrounding relation to the sharp tube for supplying the irrigation fluid to the interior of the eye. When the handpiece is in use, fluid flows through the irrigation line, through the eye and through the large bore aspiration port. This makes the system inside the eye very susceptible to any kind of fluctuation in irrigation supply and aspiration pressure. Indeed, a drop in irrigation supply or sudden increase in aspiration pressure can result in collapse of the eye because such a large bore is disposed within the eye. In addition, there is a risk that vital structures of the eye, not just cataractous tissue, will enter the large aspiration passage. Yet a further problem associated with such large bore conventional phaco probes is that material which is sucked into the constant bore aspiration passage can become clogged within the probe, requiring that the probe be removed from the patient's eye to be cleared.
Conventional phaco probes have a relatively low maximum aspiration level, approximately 60 mmHg, because of their relatively large aspiration port and the attendant risk of collapse. With such a vacuum level, it is difficult for conventional phaco probes to efficiently aspirate cataract material to the tip and hold it there while the ultrasonic vibration of the probe emulsifies it. Rather, the aspiration pressure tends to draw the cataract material towards the probe, but the ultrasonic vibration of the probe tends to push the cataract material away from the tip. These antagonistic forces make it very difficult for the practitioner to quickly and efficiently remove cataract material from within the eye. In addition, because phaco probes typically have a thin sharp distal edge, there is a very small surface area through which ultrasonic energy can be transmitted to the cataractous tissue. As a result of the size of conventional phaco probe aspiration ports, the low vacuum level and the small distal surface area, ultrasonic energy must be delivered to the probe for a relatively long period of time and at a high energy level to break up the cataractous material.
Furthermore, because of their sharp distal edges, conventional phaco probes present a significant risk of damage to the cornea, iris, and posterior capsule when inserted into the eye. This risk is increased several fold when ultrasonic energy is applied to the tip of the probe.
Thus, conventional phaco probes have a configuration which requires the lengthy application of high ultrasonic energy to break up cataractous tissue. However, the configuration of conventional probes also requires that the application of ultrasonic energy be minimized in power and duration to protect the eye from damage which can be caused by movement of the sharp tip of the probe within the eye.
The sharp tip and large bore provided on conventional phaco probes make these probes unsuitable for removal of the softer cortex of the cataract material. Thus, conventionally, phaco probes have been used to remove the harder nucleus of the cataract material and an irrigation/aspiration handpiece is used instead to remove the softer cortex of the cataract material. Such conventional irrigation/aspiration handpieces are typically rounded end probes with a hole in a top surface thereof for nudging the cortical material and aspirating the same. Such irrigation/aspiration handpieces have the disadvantage that it is difficult to direct material to be aspirated to the aspiration opening and, of course, the distinct structure and purpose of the irrigation/aspiration handpiece and the phaco probe require that two separate instruments be inserted into the eye to complete the cataract removal procedure.
Laser radiation has been used for the past several years to ablate various tissues within the eye. For example, the use of a ND:YAG laser (hereinafter referred to by the more common term, YAG laser) to remove abnormal and normal tissue has been explored. See, e.g., U.S. Pat. No. 3,971,382 to Krasnov, U.S. application Ser. No. 06/702,569 filed Feb. 19, 1985 and an article by William Steven Chambles entitled Neodymium: YAG Laser Anterior Capsulotomy and a Possible New Application, (AM Intra-Ocular Implant Society Journal, Vol. 11, January 1985). Furthermore, it has been generally recognized that laser radiation, particularly from a YAG Laser and most recently Eximer lasers, will soften cataract tissue. However, one of the difficulties with the use of laser radiation to soften cataract tissue is that fragments of the tissue are often too large or otherwise dimensioned to prevent ready passage through an aspiration opening in a probe such as used in phacoemulsification. In order to avoid making an incision which is undesirably large, that is more than the desired 2.5 to 3.5 mm, the aspirating opening must necessarily be quite small and the dimensions of the path within the probe to the vacuum source are similarly restricted. For that and other reasons, the use of laser radiation to soften cataracts for subsequent aspiration has not been practical as a standard surgical procedure.